Erasable inks

ABSTRACT

An aqueous-based erasable ink composition suitable for use in highlighters and other writing instruments includes a styrene-butadiene copolymer and a water-insoluble pigment. It preferably also includes a release agent and an anti-oxidant, and has a viscosity of between 10 cps and 30 cps.

This is a continuation of application Ser. No. 08/012,967, filed Jan. 29, 1993 now U.S. Pat. No. 5,362,167.

BACKGROUND OF THE INVENTION

The invention relates to aqueous-based erasable inks.

Aqueous-based erasable inks typically include a film-forming elastomeric polymer and colorant dispersed in water. When the inks are applied to paper, the water evaporates and the polymer provides a coalesced residue on the surface of the paper. The inks are erasable in that the residue can be removed from the paper surface for some period of time after formation without leaving a visible residue or damaging the paper.

SUMMARY OF THE INVENTION

In one aspect, the invention features a pen including a body, a writing tip at one end of the body, a reservoir included within the body, and an aqueous-based, erasable marking composition having a viscosity of between 10 cps and 30 cps (preferably between 10 cps and 20 cps) within the reservoir. The marking composition includes a latex emulsion (a rubber dispersed in water) and a water insoluble colorant, preferably a fluorescent pigment like those commonly used in highlighters. In a preferred embodiment, the pen is a marker, having a porous tip, and the marking composition is delivered to the tip by capillary action.

Preferred compositions for use in the marker include a release agent (preferably a silicone), an anti-oxidant (preferably a cresol), and a latex with a rubber solids content of between 20% and 40% and a viscosity of less than 50 cps (more preferably less than 40 cps). The composition preferably includes between about 60% and 90% (host preferably 70% and 80%) of the latex by weight. The preferred latexes include a polystyrene-butadiene copolymer having a Mooney value of at least 90.

In another aspect, the invention features an aqueous-based, erasable marking composition that includes a a styrene-butadiene copolymer having a Mooney value of greater than 100.

In another aspect, the invention features an aqueous-based, erasable marking composition that includes a styrene-butadiene copolymer, a water insoluble colorant, and a release agent.

In another aspect, the invention features an aqueous-based, erasable marking composition that includes a styrene/butadiene copolymer, a water-insoluble colorant, and an anti-oxidant.

In another aspect, the invention features an aqueous-based, erasable marking composition that includes a styrene/butadiene copolymer, a water-insoluble colorant, and sufficient water that the viscosity of the composition (at room temperature) is between about 10 cps and 30 cps, preferably between about 10 cps and 20 cps.

The erasable inks of the invention provide markings that can be readily removed from paper for a lengthy period of time (more than a year) after the ink is applied, without damaging the paper or leaving a visible residue. The inks are storage-stable, easy to manufacture, and easy to apply. The inks preferably have a low viscosity and as a result are particularly suitable for use with standard felt-tip markers that rely on a capillary feed system to draw ink from a reservoir. Thus, the inks are suitable for use in markers, which typically use fluorescent-colored pigments. One significant advantage to using the inks in markers is that when textbook pages are highlighted by a student, the highlighted portions can be erased a year later when the book is given or sold to a different student.

Other features and advantages of the invention will be apparent from the Description of the Preferred Embodiments thereof, and from the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred compositions include a styrene/butadiene copolymer, a water-insoluble colorant, a release agent, an anti-oxidant, and water.

The styrene/butadiene copolymer is the film-forming material in the composition. The preferred copolymers are unsubstituted, i.e., they lack chemical groups such as carboxyl, sulfonyl, or amino groups, and have a high modulus of elasticity. The preferred copolymers have a Mooney viscosity of greater than 90, preferably greater than 100. Copolymers with a high Mooney value are preferred because generally they tend to be less crumbly on the paper once the water evaporates, and have a greater rub resistance.

The preferred copolymers have a styrene:butadiene ratio of between 10:90 and 35:65, more preferably between 20:80 and 30:70. In general, the higher the styrene content, the more erasable the ink. If the styrene content is lower than 10%, the erasability of the ink tends to deteriorate. If the styrene content is greater than 35%, the inks may have an undesirably high viscosity.

The preferred copolymers are available as latex emulsions from Goodyear Chemicals of Akron, Ohio under the tradename PLIOLITE. The emulsion has a solids content of 30-50% and a Brookfield viscosity (25° C.) of less than about 50 cps, more preferably about 30 cps or less. The viscosity of the latex preferably is less than 50 cps, more preferably less than 40 cps. Normally, the ink compositions will include between 60% and 90%, more preferably between about agents between about 1 to about 10 percent by weight are suitable; for the more preferred release agents amounts between about 4 to about 8 percent by weight are suitable.

The anti-oxidant inhibits the oxidation, and resultant cross-linking, of the styrene/butadiene copolymer. Cross-linking is undesirable because it adversely effects the erasability performance characteristics of the ink, particularly after the inks have been exposed to direct sunlight for a significant period of time. Especially preferred are rubber antioxidants, in particular 4,4'-thiobis (6-tert-butyl-m-cresol) and 4,4'-butylidenebis (6-tert-butyl-m-cresol). Amounts of rubber antioxidant between about 1 to about 2 percent by weight of the rubber solids are normally suitable.

The compositions can include other conventional ingredients. For example, emulsifying agents such as fatty acids (preferably fatty acid diethanolamides) are normally included in the ink in amounts between about 0.3 to about 1 percent by weight to thoroughly disperse the colorant and release agent in the aqueous phase. Dispersing agents also may be included particularly to help disperse the anti-oxidant.

Sufficient water should be included in the composition so that its Brookfield viscosity (25° C.) is less than about 30 cps, more preferably between about 10 cps and 20 cps. If the viscosity is too low, the ink will tend to absorb into the paper, making erasability difficult. If the viscosity is too high, the compositions may be too thick for practical use, particularly in capillary feed systems.

The compositions generally can be prepared by blending the ingredients under conditions of high shear. The following examples illustrate the invention. Of these 70% and 80%, of the emulsion by weight. Typically, the composition should include between about 20% and 40% of solid rubber by weight. The most preferred latex emulsion is PLIOLITE LPF-2108.

The preferred colorants are fine grain sized, organic or inorganic pigments or dyes that are insoluble in water. Examples of suitable pigments include carbon blacks and prussian blues; suitable dyes include those that are nitro- or anthroquinone-based. The amount of colorant can vary but usually will not exceed about 5% of the composition by weight. The preferred colorants have a particle size of less than 3 μm.

The more preferred colorants are fluorescent pigments that provide a vibrant, read-through, erasable tracing and which can be photocopied without observing the highlighted material. The especially preferred read-through tracings are provided by including from about 3% to 5% by weight of the fluorescent pigment. Examples of suitable fluorescent pigments include the Day-Glo pigments available from the Day-Glo Color Corp. of Cleveland, Ohio and "Lumikol", from Nippon Keiko Kagaku LTD.

The release agents used in the composition provide a film between the paper surface and the marking, which may be liquid, semi-solid or solid. This film aids in lifting the marking from the surface by a rubbing action with an elastomeric eraser, providing substantially complete removal of the marking from the surface without significant detectable damage to the surface. Preferred release agents include water dispersible silicone oils or silicone surfactants. Especially preferred release agents include combinations of silicone oils and silicone surfactants and particularly combinations of glycol polysiloxanes and silicone glycol copolymers. Normally, amounts of release examples, the most preferred compositions are those described in Examples 8, 10, 15 and 17.

    ______________________________________                                         Example 1                                                                      Ingredient       % by Weight                                                   ______________________________________                                         Dispers blue.sup.1                                                                              6%                                                            Silicone oil.sup.2                                                                              2%                                                            Dow Corning 193.sup.3                                                                           2%                                                            Clindrol 200-0.sup.4                                                                            1%                                                            Santicizer 8.sup.5                                                                              1%                                                            LPF 2108.sup.6   70%                                                           Water            18%                                                           ______________________________________                                          .sup.1 A partially aqueous dispersion of blue pigment (copper                  phthalocyanine) including about 35% by weight pigment and sold under the       Tradename Dispers blue 690007 by BASF.                                         .sup.2 A release agent; available by Ruger Chem. Co.                           .sup.3 A silicone surfactant; available from Dow Chemical Co.                  .sup.4 An emulsifier; available from Clintwood Chemical Co.                    .sup.5 A plasticizer availabe from Monsanto Co.                                .sup.6 The latex. A styrene/butadiene emulsion having a styrene:butadiene      ratio of about 29:71, a total solid concentration of about 40%, and a          Mooney viscosity of greater than 100. Sold by Goodyear Tire and Rubber Co      under the Tradename Pliolite SBR Latex Product No. LPF2108.              

    ______________________________________                                         Example 2                                                                      Ingredient       % by weight                                                   ______________________________________                                         Dispers Black.sup.7                                                                             10%                                                           Dow Corning 472.sup.8                                                                            1%                                                           LPF-2108         80%                                                           Water             9%                                                           ______________________________________                                          .sup.7 A partially agenous dispersion of carbon black including about 35%      by weight carbon black and sold by BASF.                                       .sup.8 The release agent; a water dispersible glycol polysiloxane sold by      Dow Chemical Co.                                                         

    ______________________________________                                         Example 3                                                                      Ingredient      % by weight                                                    ______________________________________                                         Lucony red 3870.sup.9                                                                          5%                                                             Lucony red 3550.sup.9                                                                          5%                                                             Ethfac 391.sup.10                                                                              1%                                                             LPF-2108        80%                                                            Water           5%                                                             ______________________________________                                          .sup.9 A partially soluble aqueous dispersion of a red pigment, including      about 35% by weight pigment, and sold by BASF.                                 .sup.10 An emulsifer; a phosphate ester sold by Ethox Chemical Co.       

    ______________________________________                                         Example 4                                                                      Ingredient         % by weight                                                 ______________________________________                                         Dispers black       6%                                                         Santowhite Antioxidant.sup.11                                                                     0.56%                                                       Clindrol 200-0     0.44%                                                       Dow Corning 193     5%                                                         LPF 2108           70%                                                         Water              18%                                                         ______________________________________                                          .sup.11 Sold by Monsanto Chemical Co.                                    

    ______________________________________                                         Example 5                                                                      Ingredient        % by weight                                                  ______________________________________                                         Dispers black     6%                                                           Santowhite Antioxidant                                                                           0.56%                                                        Clindrol 200-0    0.44%                                                        DOW CORNING 193   2%                                                           Silicone fluid    3%                                                           LPF 2108          70%                                                          Water             18%                                                          ______________________________________                                    

    ______________________________________                                         Example 6                                                                      Ingredient         % by weight                                                 ______________________________________                                         Lumikol Pink Dispersion.sup.12                                                                    25%                                                         Silicone oil       2%                                                          DOW CORNING 193    2%                                                          Clindrol 200-0     1%                                                          LPF 2108           70%                                                         ______________________________________                                          .sup.12 A fluorescent pigment dispersion containing about 25% by weight o      pigment; available from Nippon Keiko Kagaku LTD.                         

    ______________________________________                                         Example 7                                                                      Ingredient       % by weight                                                   ______________________________________                                         Dispers blue     5%                                                            Water            20%                                                           Silicone oil     2%                                                            Dow Corning 193  2%                                                            Clindrol 200-0   1%                                                            LPF 2108         70%                                                           ______________________________________                                    

    ______________________________________                                         Example 8                                                                      Ingredient        % by weight                                                  ______________________________________                                         Lumikol pink dispersion                                                                          25%                                                          Silicone oil      2%                                                           DOW CORNING 193   2%                                                           Clindrol 200-0    1%                                                           Santowhite antioxidant                                                                           0.5%                                                         LPF 2108          69.5%                                                        ______________________________________                                    

    ______________________________________                                         Example 9                                                                      Ingredient       % by weight                                                   ______________________________________                                         Dispers blue     5%                                                            Water            19.5%                                                         Silicone oil     2%                                                            Dow Corning 193  2%                                                            Clindrol 200-0   1%                                                            LPF 2108         70%                                                           Santowhite antioxidant                                                                          0.5%                                                          ______________________________________                                    

    ______________________________________                                         Example 10                                                                     Ingredient          % by weight                                                ______________________________________                                         Lumikol Yellow Dispersion.sup.13                                                                   25%                                                        Silicone oil        2%                                                         Dow Corning 193     2%                                                         Clindrol 200-0      1%                                                         Ethanox 322.sup.14  0.5%                                                       LPF 2108            69.5%                                                      ______________________________________                                          .sup.13 A fluorescent pigment dispersion containing about 25% by weight        pigment; availabe from Nippon Keiko Kagaku LTD.                                .sup.14 A preferred antioxidant, available from Monsanto Chemical Co.    

    ______________________________________                                         Example 11                                                                     Ingredient        % by weight                                                  ______________________________________                                         Lumikol Pink Dispersion                                                                          25%                                                          Dow Corning 193    3%                                                          LPF 2108          55%                                                          Water             16%                                                          Clindrol 200-0     1%                                                          ______________________________________                                    

    ______________________________________                                         Example 12                                                                     Ingredient       % by weight                                                   ______________________________________                                         LPF 2108         55%                                                           Clindrol 200-0    1%                                                           Dow Corning 193   2%                                                           Water            14%                                                           Lumikol NKW 3003.sup.15                                                                         25%                                                           Drying Agent.sup.16                                                                              3%                                                           ______________________________________                                          .sup.15 A red fluorescent pigment available from Nippon Keiko Kagaku LTD.      .sup.16 Either Dowanol DB or EB; available from Dow Chemical Co.         

    ______________________________________                                         Example 13                                                                     Ingredient       % by weight                                                   ______________________________________                                         LPF 2108         40%                                                           Propylene glycol.sup.17                                                                         20%                                                           Lumikol green.sup.18                                                                            20%                                                           White.sup.19      5%                                                           Water            15%                                                           ______________________________________                                          .sup.17 An antidrying agent                                                    .sup.18 A green flurorescent pigment available from Nippon Keiko Kagaku        LTD.                                                                           .sup.19 A white pigment available from BASF.                             

    ______________________________________                                         Example 14                                                                     Ingredient      % by weight                                                    ______________________________________                                         Ethanox 322     0.56%                                                          Paraplex WP-1.sup.20                                                                           0.44%                                                          Silicone fluid  3.33%                                                          Dow Corning 193 2.67%                                                          LPF 2108          70%                                                          DWB-M 601.sup.21                                                                                 6%                                                           Water             17%                                                          ______________________________________                                          .sup.20 A plasticizer available from RohmHaas Chemical Co.                     .sup.21 Blue pigment dispersion available from Nikko Bics LTD.           

    ______________________________________                                         Example 15                                                                     Ingredient       % by weight                                                   ______________________________________                                         Anti-oxidant.sup.22                                                                             2%                                                            Clindrol 200-0   1%                                                            Dow Corning 193  3%                                                            Lumikol NKW 3007 24%                                                           LPF 2108         70%                                                           ______________________________________                                          .sup.22 Either Naugard SP antioxidant or Naugawhite antioxidant. Both are      phenols available from Uniroyal.                                         

    ______________________________________                                         Example 16                                                                     Ingredient       % by weight                                                   ______________________________________                                         Dispers blue     5%                                                            Dow Corning 193  3%                                                            Clindrol 200-0   1%                                                            Propylene glycol 1%                                                            Water            19.5%                                                         Santowhite antioxidant                                                                          0.5%                                                          LPF 2108         70%                                                           ______________________________________                                    

    ______________________________________                                         Example 17                                                                     Ingredient       % by weight                                                   ______________________________________                                         Lumikol NKW 3007 25%                                                           Dow Corning 193   3%                                                           Clindrol 200-0    1%                                                           Santowhite anitoxidant                                                                          0.5%                                                          Water            1.5%                                                          LPF 2108         69%                                                           ______________________________________                                    

The preferred inks can be used in conventional capillary feed markers that preferably include a polyester fiber tip (or nib) connected to an ink reservoir, preferably also made of polyester fiber. Other types of nibs (e.g., acrylonitrile fibers) and reservoirs (e.g., polyethylene fibers and cellulose acetate fibers) can be used. The reservoir is surrounded by, e.g., a polypropylene barrel, and is capped at the end opposite the nib with, e.g., a polypropylene plug; the marker also includes a polypropylene cap for covering the nib. The reservoirs are available from, e.g., American Filtrona Co. of Richmond, Va., or Baumgartner. The nibs are available from e.g., Aubex Co. of Tokyo, Japan, Teibow or Porex. During use, because the ink has a relatively low viscosity, the ink is drawn from the reservoir by the tip by capillary action. Passages from, for example, a textbook can be highlighted with the inks, which provide a uniform, transparent covering over the passage. The inks are erasable when applied.

The most preferred composition exhibit erasability characteristics that do not appreciably deteriorate for lengthy periods of time (at least a year). Compositions can be tested for such properties by making a mark on standard 60 lb. offset printing paper and exposing the mark to six hours of sunlight for six consecutive days. The most preferred compositions exhibit approximately the same ease of erasability of the mark using a standard Pink Pearl eraser, (available from Eberhard Faber) after seven days as two hours after application.

Other embodiments are within the claims. For example, the marking composition of the invention may be used in other types of writing instruments, e.g. ball-point pens, and in other suitable applications, e.g. bottle and brush ink dispensers. 

I claim:
 1. A writing instrument comprising an outer body; a writing tip at one end of said body; a reservoir included within said body and in fluid communication with said writing tip; and within said reservoir an aqueous-based, non-shear thinning ink that is erasable from and capable of forming a read-through tracing on 60 lb. offset printing paper, said ink comprising water, a colorant, and a styrene-butadiene copolymer having a styrene content of less than about 35%.
 2. A writing instrument of claim 1 wherein said colorant is a fluorescent colorant.
 3. A writing instrument of claim 1 wherein said ink has a viscosity of from about 10 to 30 cps.
 4. A writing instrument of claim 1 wherein said ink further comprises a release agent.
 5. A writing instrument of claim 1 wherein said ink further comprises an antioxidant.
 6. A method of providing an erasable marking on a paper substrate comprisingproviding a marker comprising an outer body; a writing tip at one end of said body; an ink reservoir included within said body and in fluid communication with said writing tip; and, within said ink reservoir, an aqueous-based ink that is erasable from 60 lb. offset paper, said ink comprising water, a colorant, and a styrene-butadiene copolymer having a styrene content of less than about 35%, and contacting said writing tip with a paper substrate to transfer said ink from said writing tip to said paper substrate to provide an erasable marking on said paper substrate.
 7. A method of claim 6 further comprising the step of erasing said erasable marking from said paper substrate.
 8. A method of claim 6 wherein said ink further comprises a release agent.
 9. A method of claim 6 wherein said colorant is a fluorescent pigment.
 10. A method of claim 6 wherein said erasable marking is a read-through tracing, made over an underlying marking to highlight said underlying marking.
 11. A method of claim 6 wherein said ink further comprises an antioxidant.
 12. A method of claim 9 wherein said erasable marking is a read-through tracing, made over an underlying marking to highlight said underlying marking.
 13. A writing instrument of claim 1 wherein said ink has a styrene-butadiene copolymer solids content less than 50% by weight.
 14. A writing instrument of claim 1 wherein said ink has a styrene-butadiene copolymer solids content between and 40% by weight.
 15. A writing instrument of claim 1 wherein said styrene-butadiene copolymer has a Mooney value of at least
 90. 16. A writing instrument of claim 1 wherein said copolymer has a styrene:butadiene ratio of between 10:90 and 35:65.
 17. The method of claim 6 wherein said ink has a styrene-butadiene copolymer solids content less than 50% by weight.
 18. The method of claim 6 wherein said ink has a styrene-butadiene copolymer solids content between 10% and 40% by weight.
 19. The method of claim 6 wherein said styrene-butadiene copolymer has a Mooney value of at least
 90. 20. The method of claim 6 wherein said copolymer has a styrene:butadiene ratio of between 10:90 and 35:65.
 21. The method of claim 6 wherein said ink has a viscosity of from about 10 to 30 cps. 